net: ipa: add IPA v5.1 and v5.5 to ipa_version_string()

Handle the case for v5.1 and v5.5 instead of returning "0.0".

Also reword the comment below since I don't see any evidence of such a
check happening, and - since 5.5 has been missing - can happen.

Fixes: 3aac8ec ("net: ipa: add some new IPA versions")
Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Reviewed-by: Dawid Osuchowski <dawid.osuchowski@linux.intel.com>
Reviewed-by: Alex Elder <elder@riscstar.com>
Link: https://patch.msgid.link/20250728-ipa-5-1-5-5-version_string-v1-1-d7a5623d7ece@fairphone.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: lweiss-fairphone

drivers/net/ipa/ipa_sysfs.c

@@ -37,8 +37,12 @@ static const char *ipa_version_string(struct ipa *ipa)
 		return "4.11";
 	case IPA_VERSION_5_0:
 		return "5.0";
+	case IPA_VERSION_5_1:
+		return "5.1";
+	case IPA_VERSION_5_5:
+		return "5.5";
 	default:
-		return "0.0";	/* Won't happen (checked at probe time) */
+		return "0.0";	/* Should not happen */
 	}
 }