rt2x00: Correct initial value of US_CYC_CNT register for pcie interface

CLOCK CYCLE: Clock cycle count in 1us
PCI:0x21, PCIE:0x7d, USB:0x1e

Signed-off-by: RA-Jay Hung <jay_hung@ralinktech.com>
Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>