MAINTAINERS: exclude gnss from SIRFPRIMA2 regex matching

Exclude the gnss subsystem from SIRMPRIMA2 regex matching, which would
otherwise match the unrelated gnss sirf driver.

Cc: Barry Song <baohua@kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

MAINTAINERS

@@ -1472,6 +1472,7 @@ F:	drivers/clk/sirf/
 F:	drivers/clocksource/timer-prima2.c
 F:	drivers/clocksource/timer-atlas7.c
 N:	[^a-z]sirf
+X:	drivers/gnss
 
 ARM/EBSA110 MACHINE SUPPORT
 M:	Russell King <linux@armlinux.org.uk>