firmware: improve description of firmware_request_nowarn

The doubled 'however' is confusing. Simplify the comment a little and
reformat the paragraph.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20200702221107.6562-1-wsa+renesas@sang-engineering.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>