samples: bpf: Ix kernel-doc syntax in file header

The opening comment mark '/**' is used for highlighting the beginning of
kernel-doc comments.
The header for samples/bpf/ibumad_kern.c follows this syntax, but
the content inside does not comply with kernel-doc.

This line was probably not meant for kernel-doc parsing, but is parsed
due to the presence of kernel-doc like comment syntax(i.e, '/**'), which
causes unexpected warnings from kernel-doc:
warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * ibumad BPF sample kernel side

Provide a simple fix by replacing this occurrence with general comment
format, i.e. '/*', to prevent kernel-doc from parsing it.
Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/bpf/20210523151408.22280-1-yashsri421@gmail.com

samples/bpf/ibumad_kern.c

 // SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
 
-/**
+/*
  * ibumad BPF sample kernel side
  *
  * This program is free software; you can redistribute it and/or

samples/bpf/ibumad_user.c

 // SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
 
-/**
+/*
  * ibumad BPF sample user side
  *
  * This program is free software; you can redistribute it and/or