staging: r819xU_phy: Remove some local variables from the stack

staging: r819xU_phy: Remove some local variables from the stack

Fixes the following W=1 kernel build warning(s):

 drivers/staging/rtl8192u/r819xU_phy.c: In function ‘rtl8192_phy_SwChnlStepByStep’:
 drivers/staging/rtl8192u/r819xU_phy.c:1328:1: warning: the frame size of 1096 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michael Straube <straube.linux@gmail.com>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210414181129.1628598-6-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>