usb: gadget: s3c-hsotg: fix CodingStyle issues

checkpatch.pl has some valid complaints about style in s3c-hsotg.c:
- macro with 'if' should be really enclosed in 'do {} while (0)'
- seq_puts() is going to be slightly faster than seq_printf()
- pr_err() is shorter than printk(KERN_ERR ...)

Signed-off-by: Pavel Machek <pavel@denx.de>
[bzolnier: minor fixes]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>