staging: greybus: Replace __attribute__((packed)) by __packed in various instances

This patch makes the following changes:
 * Replaces '__attribute__((packed))' by '__packed' in various locations
   to remove checkpatch warning

Signed-off-by: Jonathan Bergh <bergh.jonathan@gmail.com>
Link: https://lore.kernel.org/r/20240227160113.111264-1-bergh.jonathan@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: icojb25

drivers/staging/greybus/greybus_authentication.h

@@ -44,7 +44,7 @@
 /* IOCTL support */
 struct cap_ioc_get_endpoint_uid {
 	__u8			uid[8];
-} __attribute__ ((__packed__));
+} __packed;
 
 struct cap_ioc_get_ims_certificate {
 	__u32			certificate_class;
@@ -53,7 +53,7 @@ struct cap_ioc_get_ims_certificate {
 	__u8			result_code;
 	__u32			cert_size;
 	__u8			certificate[CAP_CERTIFICATE_MAX_SIZE];
-} __attribute__ ((__packed__));
+} __packed;
 
 struct cap_ioc_authenticate {
 	__u32			auth_type;
@@ -64,7 +64,7 @@ struct cap_ioc_authenticate {
 	__u8			response[64];
 	__u32			signature_size;
 	__u8			signature[CAP_SIGNATURE_MAX_SIZE];
-} __attribute__ ((__packed__));
+} __packed;
 
 #define CAP_IOCTL_BASE			'C'
 #define CAP_IOC_GET_ENDPOINT_UID	_IOR(CAP_IOCTL_BASE, 0, struct cap_ioc_get_endpoint_uid)