ACPI: APEI: Remove redundant assignments in erst_dbg_{ioctl|write}()

ACPI: APEI: Remove redundant assignments in erst_dbg_{ioctl|write}()

Use the result of copy_from_user() directly instead of assigning it to
the local variable 'rc' and then overwriting it in erst_dbg_write() or
immediately returning from erst_dbg_ioctl().

No intentional functional changes.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Link: https://patch.msgid.link/20250903224913.242928-2-thorsten.blum@linux.dev
[ rjw: Changelog edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>