ARM: bcm2835: Fix grammar in help message

Replace "is use" by "is used" and remove a comma.

Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Jiri Kosina <trivial@kernel.org>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>