security/commoncap: Use xattr security prefix len

Using the existing defined XATTR_SECURITY_PREFIX_LEN instead of
sizeof(XATTR_SECURITY_PREFIX) - 1. Pretty simple cleanup.
Signed-off-by: Carmeli Tamir <carmeli.tamir@gmail.com>
Signed-off-by: James Morris <jamorris@linux.microsoft.com>

security/commoncap.c

@@ -920,7 +920,7 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name,
 
 	/* Ignore non-security xattrs */
 	if (strncmp(name, XATTR_SECURITY_PREFIX,
-			sizeof(XATTR_SECURITY_PREFIX) - 1) != 0)
+			XATTR_SECURITY_PREFIX_LEN) != 0)
 		return 0;
 
 	/*
@@ -952,7 +952,7 @@ int cap_inode_removexattr(struct dentry *dentry, const char *name)
 
 	/* Ignore non-security xattrs */
 	if (strncmp(name, XATTR_SECURITY_PREFIX,
-			sizeof(XATTR_SECURITY_PREFIX) - 1) != 0)
+			XATTR_SECURITY_PREFIX_LEN) != 0)
 		return 0;
 
 	if (strcmp(name, XATTR_NAME_CAPS) == 0) {