cnss2: Always use firmware_request_nowarn() to load binaries

The sysfs fallback mechanism is enabled if direct filesystem
lookup fails, so always use firmware_request_nowarn() instead
of request_firmware() to avoid unnecessary warning logs. Driver
will only check for return code of the API.

Change-Id: I3bdbd23d6e23384bfcb7dc2fa32712fc5af79d03
Signed-off-by: Yue Ma <yuem@codeaurora.org>