pinctrl: sirf: fix the pins of sdmmc5 connected with TriG

sdmmc5 has only 3 pins CMD, CLK, DATA which are connected with CSR
TriG RF multi-GNSS. The hardware connection is like:
DATA -- GPS_SGN
CLK  -- GPS_RF_CLK
CMD  -- GPS_MAG
here we drop redundant pins in sdmmc5 group.

Signed-off-by: Bin Shi <Bin.Shi@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>