ram: ast2600: Fix incorrect statement of the register polling

The condition "~data" in the if-statement is a typo.  The original
intention is to poll if SDRAM_PHYCTRL0_INIT bit equals to 0. So use
"data == 0" for instead.

Besides, the bit[1] of "phy_status" register is hardwired to
SDRAM_PHYCTRL0_INIT (with inverse logic). Since SDRAM_PHYCTRL0_INIT has
already done, remove the unnecessary checking of phy_status[1].

Fixes: fde93143 ("ram: aspeed: Add AST2600 DRAM control support")

Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>