capsule: Fix EC version detection for Zephyr based

Now it can work for both legacy and zephyr based ECs.
Tested on Intel 12th gen, AMD Ryzen 7040, AMD Ryzen AI 300, Framework Desktop.

```
> framework_tool --h2o-capsule Framework_Laptop_13_Ryzen7040_capsule_signed_allsku_3.08.cap
[...]
EC
  Type:                         RO
  Version:    azalea_v3.4.113382-ec:ec916d,os
  RollbackVer:                   0
  Platform:                 azalea
  Version:              3.4.113382
  Commit:                   ec916d
  Size:                     258048 B
  Size:                        252 KB
EC
  Type:                         RW
  Version:    azalea_v3.4.113382-ec:ec916d,os
  RollbackVer:                   0
  Platform:                 azalea
  Version:              3.4.113382
  Commit:                   ec916d
  Size:                     258048 B
  Size:                        252 KB
[...]
```

Signed-off-by: Daniel Schaefer <dhs@frame.work>

Author: JohnAZoidberg

framework_lib/src/capsule_content.rs

@@ -44,12 +44,10 @@ pub fn find_bios_version(data: &[u8]) -> Option<BiosCapsule> {
 }
 
 pub fn find_ec_in_bios_cap(data: &[u8]) -> Option<&[u8]> {
-    let needle = b"_IFLASH_EC_IMG_";
-    let found_iflash = util::find_sequence(data, needle)?;
-    // The actual EC binary is a few bytes after `_IFLASH_EC_IMG_`.
-    // Just earch for the first 4 bytes that seem to appear in all EC images.
-    let found = util::find_sequence(&data[found_iflash..], &[0x10, 0x00, 0x00, 0xf7])?;
-    Some(&data[found_iflash + found..found_iflash + found + EC_LEN])
+    let needle = b"$_IFLASH_EC_IMG_";
+    let found = util::find_sequence(data, needle)?;
+    let ec_offset = found + 0x9 + needle.len() - 1;
+    Some(&data[ec_offset..ec_offset + EC_LEN])
 }
 
 pub fn find_pd_in_bios_cap(data: &[u8]) -> Option<&[u8]> {