fs/reiserfs/inode: remove dead code in _get_block_create_0()

Since commit 27b3a5c5 ("kill-the-bkl/reiserfs: drop the fs race
watchdog from _get_block_create_0()"), which removed a label that may
have the pointer 'p' touched in its control flow, related if statements
now eval to constant value now. Just remove them.

Assigning value NULL to p here
293     char *p = NULL;

In the following conditional expression, the value of p is always NULL,
As a result, the kunmap() cannot be executed.
308	if (p)
309		kunmap(bh_result->b_page);

355	if (p)
356		kunmap(bh_result->b_page);

366	if (p)
367		kunmap(bh_result->b_page);

Also, the kmap() cannot be executed.
399	if (!p)
400		p = (char *)kmap(bh_result->b_page);

[JK: Removed unnecessary initialization of 'p' to NULL]

Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220720083029.1065578-1-zengjx95@gmail.com