mmc: sdhci-s3c: Use shifts to divide by powers of two

Current implementation of sdhci_s3c_consider_clock() is highly
inefficient due to multiple integer divisions by variable performed in a
loop. Since only divisors that are powers of two are considered, this
patch replaces them with respective shifts, removing all the integer
divisions.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by; Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <chris@printf.net>