ASoC: cs-amp-lib: Return attributes from cs_amp_get_efi_variable()

ASoC: cs-amp-lib: Return attributes from cs_amp_get_efi_variable()

Add a pointer argument to cs_amp_get_efi_variable() to optionally
return the EFI variable attributes.

Originally this function internally consumed the attributes from
efi.get_variable(). The calling code did not use the attributes
so this was a small simplification.

However, when writing to a pre-existing variable we would want to
pass the existing attributes to efi.set_variable(). This patch
deals with the change to return the attribute in preparation for
adding code to update the variable.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20251021105022.1013685-8-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>