ppp: Adjust indentation into ppp_async_input

Clang warns:

../drivers/net/ppp/ppp_async.c:877:6: warning: misleading indentation;
statement is not part of the previous 'if' [-Wmisleading-indentation]
                                ap->rpkt = skb;
                                ^
../drivers/net/ppp/ppp_async.c:875:5: note: previous statement is here
                                if (!skb)
                                ^
1 warning generated.

This warning occurs because there is a space before the tab on this
line. Clean up this entire block's indentation so that it is consistent
with the Linux kernel coding style and clang no longer warns.

Fixes: 6722e78c ("[PPP]: handle misaligned accesses")
Link: https://github.com/ClangBuiltLinux/linux/issues/800


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>